1. Technical Field
The present invention relates to an indicated position detection sensor of an electromagnetic induction indicator position detector used as an input device of electronic equipment such as tablet terminal.
2. Description of the Related Art
Recent years have seen the use of electromagnetic induction position input devices as input devices for tablet terminals and intelligent mobile phone terminals called smartphones. These position input devices each include a position indicator and indicator position detector. The position indicator is in the shape of a pen (pen-shaped position indicator). The indicator position detector has an input surface, on which pointing operation is performed, and text, graphics and other information is entered using the pen-shaped position indicator. The pen-shaped position indicator includes a resonance circuit made up of a coil and capacitor. On the other hand, the indicator position detector includes a position detection sensor. The position detection sensor includes X- and Y-axis direction loop coil groups that overlap one another. The X-axis direction loop coil group is formed by arranging a plurality of loop coils horizontally (in the X-axis direction). The Y-axis direction loop coil group is formed by arranging a plurality of loop coils vertically (in the Y-axis direction).
Then, one loop coil is selected in a predetermined sequence from among the plurality of loop coils arranged in the position detection sensor area, after which a transmission signal is transmitted from the selected loop coil to the pen-shaped position indicator, thus allowing the capacitor of the pen-shaped position indicator to be charged. Next, the loop coil used for the transmission is connected to a reception circuit, thus receiving a signal from the resonance circuit of the pen-shaped position indicator and detecting the indicated position based on the reception signal. Such an exchange of signals is performed by sequentially changing the loop coils, thus allowing detection of the position indicated by the pen-shaped position indicator on the position detection sensor.
It should be noted that a calculation method based on the reception signal levels of three loop coils, i.e., the coil with the highest reception signal level from the pen-shaped position indicator, and the two other coils, one on each side of the above coil, is known as a calculation method for an electromagnetic induction position input device to calculate a position. Normally, the position of the pen-shaped position indicator is calculated based on the reception signals of three loop coils (three-point detection method). Further, Japanese Patent Laid-Open No. Hei 5-181594 described later discloses an invention that uses another calculation method in combination with the three-point detection method because it is difficult to obtain reception signals from three loop coils in the areas surrounding the position detection sensor (vertical and horizontal areas surrounding the position detection sensor). This method calculates the position of the pen-shaped position indicator based on reception signal levels of two loop coils (two-point detection method).
This two-point detection method makes it possible to reduce the size of the area surrounding the position detection sensor where it has been difficult to detect the position of the pen-shaped position indicator. In the areas near the edge portions of the position detection sensor that are further outside the areas surrounding the position detection sensor, it is possible to obtain a reception signal from only a single loop coil. Therefore, this area near the edge portions of the position detection sensor where the position indicated by the pen-shaped position indicator can be detected by only a single loop coil has been treated as a so-called disabled (invalid) area.
It should be noted that an electromagnetic induction position input device is used not only as an external input device for a PC (personal computer) but also as an input device for a tablet terminal and intelligent mobile phone terminal as described earlier. In this case, the electromagnetic induction position input device is arranged to be stacked on a display element such as LCD (liquid crystal display), thus allowing it to be integral with the tablet terminal PC or intelligent mobile phone terminal.